Swedish patent specifications 7706927-6, 7908805-0 and 8105501-4 disclose systems in which the type of heat exchanger intended for use in practicing the present invention is used. These systems are completely open. For the heat exchanger included in such a system to function it is required that the heat exchanger be sunk to a certain proper level in the liquid, consisting of the polluted water or sea/lake water, which surrounds the cylindrical panels in the presence of variable flow. If this is not possible, overflow pipes or water traps must be used to keep the liquid level in the heat exchanger at the proper level. This involves a large disadvantage, since placing and erection of the heat exchanger are thus decided within certain limits, in turn resulting in that large difficulties in the use of available space can occur in fitting the heat exchanger into the system.
By means of the present invention it is possible to place the heat exchanger in such a location that it is suitable in the system, e.g. without regard to the liquid level in an open system.